Optical systems that combine reflective optics with refractive optics are known. For example, U.S. Pat. No. 7,049,597, issued to Bodkin, and U.S. Pat. No. 7,119,969, issued to Amon, disclose a dual optical path with reflective and refractive elements for use in a dual spectrum optical system. Each optical system includes one optical system for visible imaging and another optical system for hyperspectral imaging. A beam splitter is used to form two optical paths.
U.S. Pat. No. 5,051,830, issued to Von Hoessle, discloses a refractive lens with inner and outer zones is disclosed. Light from the outer zone travels to a reflective lens which focuses the light onto a first sensor. Light from the inner zone is focused onto a second sensor that is located in a back to back configuration with the first sensor. A single electronic system is used to support both imaging systems so that only one of the imaging systems can be used at a time. The positioning of the two sensors is designed to minimize weight in a guided missile application. The shorter focal length imaging system is provided for general guidance of the missile to the target. The longer focal length imaging system is provided for more accurate guidance of the missile during the final stage of guidance of the missile to the target.
U.S. Pat. No. 6,870,690, issued to Lawson, discloses a lens in which an outer portion of the lens is designed for one spectral band and an inner portion of the lens is designed for another spectral band. U.S. Pat. No. 5,172,235, issued to Wilm, discloses two lenses that are focused onto one sensor. Complimentary zone filters enable the two images from the two lenses to overlay one another to produce a composite image with different areas of resolution.
There is still a need, however, to provide a compact imaging system incorporating a dual focal length lens system that includes two independent lens systems that simultaneously provide different focal length images of the same scene or object.